The invention resides in a valve for the dosed discharge of fluids, particularly an injection valve for fuel injection systems of internal combustion engines wherein the valve is operated by a stack of piezo elements.
DE 195 00 706 A1 discloses a fuel injection valve for internal combustion engines, which valve includes a hydraulic stroke amplifier for increasing the stroke length of a piezo electric actuator. In this valve, fluid supply passages and fluid return passages are separated. The fluid is supplied to an annular space by way of a passage disposed in the valve housing.
It is however, a disadvantage that, during the supply of the fuel to the annular space, the passage subjects the fuel injection valve to bending tensions.
EP 0 218 895 B1 relates to a dosing valve for dosing fluids. This prior art dosing valve includes a piezo electric control member and a stack of piezo elements of a length that can be changed by the application of a control voltage. At one end, the stack of piezo elements is connected to a valve needle, and, at its opposite end, it is exposed to a liquid-filled damper space delimited by a damper piston. The damper piston is movable in the direction of the axis of the stack of piezo elements and is so designed and arranged in a housing that it is firmly held in position relative to housing when the length of the stack of piezo elements is changed by the control voltage applied thereto. By a contraction of the stack of piezo elements, the valve needle is lifted of the valve seat.
In this arrangement, the fuel to be injected into the combustion chamber of the internal combustion engine is supplied to the end of the valve housing remote from the combustion chamber and, from there, flows through a passage to the annular space which is formed between the lower end portion of the valve and the stack of piezo elements disposed therein. From here, the fuel is conducted to another annular space which is limited by the valve housing wall and the valve needle. Then the fuel flows into an annular space adjacent the valve discharge opening closed by the valve needle.
In this arrangement, the stack of piezo elements is exposed directly to the pressure of the fuel supplied to the valve. This pressure has a value of ca. 1000 bar so that the stack of piezo elements is compressed and shortened to such a degree that an accurate functioning of the valve is not insured because of the control length loss of the stack of piezo elements under pressure.
In addition, the injection time for the injection of the fuel into the combustion chamber is not accurately controllable since, after lift off of the valve needle from the valve seat, the fuel enters through the gap formed thereby into the combustion chamber in an uncontrolled manner.
It is the object of the present invention to provide a valve which permits ejection of a fluid in a well defined manner and to insure accurate operation of the piezo-electric valve even at very high injection pressures.